Gasifier for a solid carbon fuel

ABSTRACT

Disclosed here are example gasifiers for gasification of solid carbon fuel. An example gasifier includes a vertical vessel that includes feeding means for introducing a fuel at a top and along a first vertical axis in the vessel. The example vessel also includes a pyrolysis zone for pyrolysis of the fuel, a combustion zone for burning pyrolysis gases from the pyrolysis zone, a reduction zone for gasifying carbonized fuel from the pyrolysis zone and an outlet for collecting gases produced in the reduction zone. In addition, the example vessel includes a horizontal plate fixedly mounted between the feeding means and the pyrolysis zone for receiving and retaining the fuel introduced into the vessel. Also, the example vessel includes a movable pusher mounted between the feeding means and the horizontal plate, the movable pusher to push the fuel retained on the horizontal plate into the pyrolysis zone and positioned or positionable above the horizontal plate.

RELATED APPLICATIONS

This patent is a continuation of International Patent Application SerialNo. PCT/EP2012/067349, filed on Sep. 5, 2012, which claims priority toEuropean Patent Application 11180062.9, filed on Sep. 5, 2011, both ofwhich are hereby incorporated herein by reference in their entireties.

TECHNICAL FIELD

This disclosure relates generally to gasifiers and, more specifically toa gasifier for gasification of a solid carbon fuel, such as, forexample, solid biomass.

BACKGROUND

Known gasifiers make it possible to produce a fuel gas starting from asolid carbon fuel, in particular starting from wood waste, such as thatobtained, for example, from sawmills or from logging operations, orstarting from agricultural byproducts (straw, etc.), or also fromrecycled wood. This fuel gas contains carbon monoxide and hydrogen andcan subsequently be used for various purposes such as, for example, feedfor a gas turbine or an internal-combustion engine, a boiler, or afurnace.

To feed a vessel with fuel, it is known to provide fuel feeding meansthat are impervious to the gases that will be produced in the vessel.This hermeticity prevents the gases produced in the vessel from enteringthe systems for fuel storage and feed, so that said gases will traveltoward the outlet when the gasifier is in operation.

Use of a lock mechanism at the inlet of the first vessel for thispurpose is known.

Patent application WO 2007/081296 mentions a gasifier that includes arotary valve located in the upper part of the reactor. This deviceoffers proper metering of fuel feed, but it does have the drawback thatit is not sufficiently impervious to the gases and requires anadditional sealing mechanism upstream, which increases its cost.Moreover, the valve must be able to withstand the high temperaturesprevailing in the first vessel when the gasifier is in operation, whichrequires valves that are particularly expensive.

Other mechanisms only employ a double flap sluice in place of the rotaryvalve discussed above. Besides the fact that this type of mechanism isless efficient with respect to the metering of material (batchmetering), the bottom flap must also withstand said high temperaturesand is therefore expensive.

Patent application WO 2001/051591 mentions a gasifier that includes alock arranged laterally relative to the upper part of the reactor, whichcan provide good hermeticity against the gases. This patent applicationalso mentions a lateral conduit equipped with an endless screw providingthe connection between the lock and the first vessel, which alsoprovides proper metering of the feed of material. However, such a deviceis expensive and unwieldy. The endless screw is also liable to becomefouled, which requires maintenance, and/or to become blocked with piecesof fuel. Moreover, as the end of the screw opens into the vessel, it issubjected to the high temperatures prevailing there when the gasifier isin operation, which makes it necessary to use an expensive screw.

Patent application WO 2010/109501 mentions a gasifier in the form of avessel, in the upper part of which the fuel is introduced laterally. Thefuel is then retained in a drying zone of the vessel by means of ahorizontal partition with a central hole. An endless screw is mountedvertically through this hole for transferring the fuel from the dryingzone to a pyrolysis zone located directly underneath the horizontalpartition. This endless screw opens into the pyrolysis zone and must beable to withstand the high temperatures prevailing there when thegasifier is in operation, which requires screws that are particularlyresistant and expensive. The endless screw is also liable to becomefouled, which requires maintenance, and/or to become blocked with piecesof fuel.

SUMMARY

One aim of the teachings of the present disclosure is to solve, at leastpartially, the problems with the gasifiers mentioned above.

For this purpose, an example gasifier according to the teachings of thisdisclosure includes a first vessel that includes a movable pushermounted between feeding means and a horizontal plate. In this example,the movable pusher is designed for pushing the fuel retained on thehorizontal plate into a pyrolysis zone and is positioned or positionableabove the horizontal plate.

With this configuration, the horizontal plate forms a thermal screenthat protects both the fuel feeding means and the pusher against thehigh temperatures prevailing in the first vessel (such as, for example,against the radiation and the flames in particular). This makes itpossible to use material transfer mechanisms (e.g., the feeding meansand/or the pusher) that are less expensive and/or increase theirdurability and/or their reliability.

A movable pusher of this example also takes up less space vertically andis simpler and more reliable than the vertical endless screw (12)proposed in patent application WO-2010/109501.

In some examples, the movable pusher includes at least one arm extendinghorizontally above the plate and mounted rotatably about a secondvertical axis. A rotary pusher allows better distribution of the fuel onthe fuel bed in the pyrolysis zone, which improves the quality of thepyrolysis reaction. This can reduce the tar content of the gas produced.

Some mechanisms were devised in the past for distribution of the fuel onthe fuel bed after the fuel is fed into the first vessel.

For example, U.S. Pat. No. 5,755,837 proposes equipping an upper part ofa vessel with an inclined channel. However, this device will causegreater accumulation of material at the points where it falls onto thefuel bed. In particular, the level of fuel will be greater at theperiphery of the first vessel than in its central part.

Also, British Patent GB 696682, proposes equipping an upper part of avessel with a mechanism with two perforated rotating plates. Here onceagain, the fuel will be placed opposite the holes. Moreover, thismechanism is liable to become fouled and/or to become blocked withpieces of fuel.

The example gasifier according to the teachings of this disclosure hasadvantages over these known devices. For example, the example gasifierdisclosed herein includes levelling means that are adapted to at leastpartially level a top surface of a bed of solid fuel in the pyrolysiszone. The examples disclosed herein include a mechanism acting directlyon the fuel bed rather than acting on the pouring of fuel onto the bed,thus reducing or eliminating the drawbacks of the known mechanisms. Thelevelling means can give even better distribution of the fuel on thefuel bed in the pyrolysis zone, which improves the quality of thepyrolysis reaction.

According to an example disclosed herein, the levelling means includesat least one arm extending horizontally at a level of a top surface ofthe bed of solid fuel in the pyrolysis zone. In this example, the atleast one arm is mounted rotatably about a third vertical axis C. Thisconstitutes a simple, reliable and effective means for distributing thesolid material more uniformly on the bed of material in the pyrolysiszone.

BRIEF DESCRIPTION OF THE DRAWINGS

These aspects as well as other aspects of the disclosure will beclarified in the detailed description of particular examples disclosedherein, reference being made to the drawings in the figures, where:

FIG. 1 shows schematically a front section of an example gasifieraccording to the teachings of this disclosure;

FIG. 2 shows schematically a front section of another example gasifieraccording to the teachings of this disclosure;

FIG. 3 shows schematically a cross section of the gasifier in FIG. 2;

FIG. 4 shows schematically a front section of another example a gasifieraccording to the teachings of this disclosure;

FIG. 5 shows schematically a front section of another example gasifieraccording to the teachings of this disclosure;

FIG. 6 shows schematically a cross section of the gasifier in FIG. 5;

FIGS. 7 a and 7 b show schematically a front section and cross section,respectively, of another example a gasifier according to the teachingsof this disclosure;

FIGS. 8 a and 8 b show respectively a front section and a cross sectionof another example gasifier according to the teachings of thisdisclosure.

The drawings in the figures are not to scale. Generally, similarelements are denoted by similar references in the figures.

DETAILED DESCRIPTION

Disclosed herein are example gasifiers that include at least one firstvertical vessel equipped with feeding means for introducing fuel at atop and along a first vertical axis in the first vessel. The examplevessel includes a pyrolysis zone wherein the fuel undergoes pyrolysis, acombustion zone for burning pyrolysis gases from the pyrolysis zone, areduction zone for gasifying the carbonized fuel from the pyrolysiszone, and an outlet for collecting gases produced in the reduction zone.The example first vessel further comprising a horizontal plate mountedfixedly between the feeding means and the pyrolysis zone for receivingand retaining the fuel fed into the vessel.

Also disclosed herein are example units for production and combustion ofgas that include the example gasifiers disclosed herein for producingthe gas.

The examples disclosed herein relate to a co-current fixed-bed gasifier,formed by a single vessel simultaneously including the pyrolysis zone,the combustion zone and the reduction zone. The teachings of thisdisclosure, however, are not limited to this type of gasifier butrelates to all gasifiers having features of the claims, such as forexample counter-current gasifiers, and/or gasifiers that include severalvessels in succession, the first vessel being the one where thereactions of pyrolysis of the fuel take place.

The examples disclosed herein use solid biomass as an example of fuel,in some examples, any other type of solid carbon fuel will also besuitable.

FIG. 1 shows schematically a front section of an example gasifier (1)according to the teachings of this disclosure. In this example, theexample gasifier (1) is a co-current fixed-bed gasifier. This gasifieris formed by a reactor in the form of a vertical vessel (4) comprisingsuccessively, from top to bottom:

-   -   an inlet lock (5) for introducing the biomass (2) into the        vessel along a first vertical axis (A),    -   a pyrolysis zone (10) for pyrolysis of the biomass introduced        into the vessel,    -   a combustion zone (20) for burning the pyrolysis gases from the        pyrolysis zone,    -   a reduction zone (30) for gasifying the carbonized biomass from        the pyrolysis zone,    -   an outlet (6) for collecting the gases from the reduction zone,        and    -   a zone (40) for collecting and removing the ash.

In some examples, the inlet lock (5) has multiple other forms, forexample a rotary valve and/or a double flap sluice and/or any othersuitable introducing means.

The biomass (2), for example wood chips, is introduced into the vessel(4) at the top via the inlet lock (5). The biomass (2) arrives - via theintermediate device (50, 51) described in more detail below - in thepyrolysis zone (10), where the biomass (2) decomposes, under the effectof the heat, into volatile matter and into a carbon-rich solid residuegenerally called “char” or “coke”. This reaction typically takes placein a temperature range between 300° C. and 700° C.

In order to reach these temperatures, the vessel includes first meansfor admission of a pyrolysis agent (11)—for example one or morenozzle(s) opening laterally in the vessel at the level of the pyrolysiszone—and which make it possible to introduce a gas there which willsupply, directly or indirectly, the energy required for decomposition ofthe biomass into volatile matter and “char”. The pyrolysis agent can be,for example, a reactive gas containing oxygen which, by burning afraction of the biomass or of the products of decomposition of thebiomass, will release the energy to implement, effect or performpyrolysis. The pyrolysis agent may also be an inert gas (such as carbondioxide, nitrogen, steam) which, when preheated, will supply the energyto implement, effect or perform pyrolysis. It can also be a combinationof these two types of gases.

The “char” is then transferred to the reduction zone (30) by means thatare well known, for example those described in European PatentApplication EP11171156.

The volatile matter (also called “pyrolysis gases”) entering thecombustion zone (20) is burned there partially or completely. To promotethis combustion, the example vessel includes second means for admissionof a gasifying agent (21). These second means of admission can include,for example, one or more nozzle(s) opening laterally in the vessel atthe level of the combustion zone. “Gasifying agent” is to be understoodas a gas capable of reacting with the carbon and/or with the hydrogencontained in the solid fuel. Therefore the gasifying agent can be, forexample, the ambient air, a gas with higher oxygen concentration, steam,carbon dioxide or else a mixture of these gases. This combustionproduces carbon dioxide (CO₂), water (H₂O), and heat. Typically,temperatures above 1100° C. can be reached in the combustion zone.

The “char” that was transferred into the reduction zone will react withthe combustion products to form carbon monoxide (CO) and hydrogen (H₂).

In the case, for example, of an autothermal reaction of lignocellulosicmaterials—such as wood—and the use of ambient air at ambient temperatureas gasifying agent, this reaction typically takes place in a temperaturerange between 300° C. and 800° C. However, it will be possible for thistemperature to be higher and reach or even exceed 1300° C. in the casewhen a fuel richer in carbon is used and/or when preheated reagents areused. The gases produced by this reaction will be collected at theoutlet (6) of the reactor, which is located at the bottom of the vessel(4). At the outlet (6), there is a combustible gas including about 15%to about 30% of CO, about 10% to about 25% of Hz, about 0.5 to about 3%of CH₄, about 5% to about 15% of CO₂ and about 49% of N₂ when ambientair is used as gasifying agent.

The ash can be collected at the bottom (40) of the vessel.

Turning to the example device (50, 51) that is located just below theinlet lock (5), this device includes a horizontal plate (50) mountedfixedly between the inlet lock (5) and the pyrolysis zone (10). Theexample plate (50) is positioned and dimensioned to receive and retain,at least partially, the fuel (2) introduced into the vessel (4) via theinlet lock (5).

In some examples, the plate is positioned and dimensioned so that theplate retains the fuel completely and so that the latter can only flowto the pyrolysis zone under an external action, such as under the actionof the pusher described below.

For this purpose, the position and size of the plate will be adapted tothe flow properties of the fuel used, in particular its slope angle(e.g. for wood chips, the slope angle is of the order of 60°).

The example device further includes a movable pusher (51) mountedbetween the inlet lock (5) and the horizontal plate (50). The pusher(51) is positioned above the horizontal plate (50), so that thehorizontal plate forms a thermal screen protecting the pusher from theheat prevailing underneath the plate when the gasifier is operating. Asshown in the FIG. 1, the pusher (51) may include, for example, ahorizontal jack, at the end of which a vertical plate is mounted, whichacts as the pusher. When the jack is actuated, the fuel retained on theplate will be pushed by the vertical plate and will drop by gravity intothe pyrolysis zone (10). Metering of the fuel can be achieved bycontrolling the movement of the jack.

FIG. 2 shows schematically a front section of another example gasifieraccording to the teachings of this disclosure. According to thisexample, the movable pusher (51) includes at least one arm (52)extending horizontally above the horizontal plate (10) and mountedrotatably about a second vertical axis (B). This arm can include, forexample, a vertical plate.

Here, one end of the example arm is connected to a shaft of a motor (M)for rotating the arm. The movable pusher (51, 52) is positionable abovethe horizontal plate (50), which allows the plate to perform its role ofthermal screen when the pusher is effectively positioned above theplate. In this example, the pusher can temporarily project beyond theplate when the motor (M) is started, and the pusher can at some point intime be positioned above the plate.

In some examples, the motor (M) is equipped with reduction gearing inorder to increase the torque and the precision of the movementtransmitted to the first arm. In some examples, the motor (M) is mountedabove the plate so that the plate also forms a thermal screen withrespect to the motor. Also, in some examples, the motor (M) is mountedoutside the vessel, in which case the motor shaft passes through theupper part of the vessel via a seal or a sealed bearing and is connectedto the first arm (case not shown).

In some examples, the second axis (B) is offset relative to the firstaxis (A).

FIG. 3 shows schematically a cross section of the example gasifier inFIG. 2. This shows an example of the possible form of the horizontalplate (50) and arm (52) of the pusher and how these two elements can bearranged relative to one another.

In some examples, the gasifier includes a motor (M) for driving the atleast one arm (52) of the pusher in rotation about the second axis (B)and first controlling means (60) suitable for controlling the motor (M)to give a rocking, oscillation or rotating motion to the at least onearm (52) about the second axis (B). For this, it is possible for exampleto use a motor with reversible rotational directions such as, forexample, a direct-current motor.

This makes it possible to cause the biomass to overflow from a first end(56) of the plate when the motor rotates in a first direction ofrotation and to cause the biomass to overflow from a second end (57) ofthe plate, opposite the first side, when the motor rotates in a seconddirection of rotation opposite to the first direction of rotation. Thismakes it possible to obtain a more uniform distribution of the fuel onthe bed in the pyrolysis zone.

In some examples, the first controlling means (60) are able to set aninitial angular position (P1) as well as an amplitude (A1) of therocking, oscillation or rotating motion, which allows even more precisecontrol of the transfer of biomass from the plate to the pyrolysis zone.For this purpose, it is possible for example to employ a stepping motorequipped with an encoder wheel for the angular position of the motorshaft as well as a suitable controller.

FIG. 4 shows schematically a front section of another example gasifieraccording to the teachings of this disclosure.

Here, the example first vessel (4) further includes levelling means (70)suitable for at least partially levelling a top surface (80) of the bedof biomass in the pyrolysis zone (10). As shown in the figure, theselevelling means includes for example a horizontal jack whose end isequipped with a scraper. The example scraper is located at the level ofthe top surface (80) of the bed of biomass in the pyrolysis zone (10).In some examples, the scraper is in the form of a rake that has teethdirected downwards. Actuation of the jack makes it possible to level thetop surface (80) of the bed of biomass.

FIG. 5 shows schematically a front section of another example gasifieraccording to the teachings of this disclosure. According to thisexample, the levelling means (70) comprise at least one levelling arm(71) extending horizontally at the level of the top surface (80) of thebed of solid fuel in the pyrolysis zone (10). The example at least onelevelling arm (71) is mounted rotatably about a third vertical axis (C).The levelling arm can include, for example, a vertical plate and/or arake with teeth directed downwards.

Here, one end of the levelling arm (71) is connected to a shaft of amotor (M) for rotating the arm (71). In some example, the motor (M) isequipped with reduction gearing in order to increase the torque and theprecision of the movement transmitted to the arm (71). Operation of themotor makes it possible to level the top surface (80) of the bed ofbiomass when the example gasifier is in operation.

FIG. 6 shows schematically a cross section of the example gasifier inFIG. 5. This gives a better view of the levelling arm (71) and itsrotary movement.

In some examples, the levelling means includes six arms mounted radiallyat intervals of 60 degrees around a rotating shaft with axis C.

In some examples, axis B and axis C coincide. Also, in some examples,the at least one arm (52) of the pusher and the at least one arm (71) ofthe levelling means are mounted on one and the same rotating shaft (75).One such example is presented in FIGS. 7 a and 7 b.

As shown in FIGS. 7 a and 7 b, a single motor (M3) simultaneously drivesthe arm (52) of the pusher and the levelling arm (71) via a commonrotating shaft (75), which simplifies assembly and therefore makes itless expensive, less bulky and more reliable.

In such a configuration, the arm (52) of the pusher and the levellingarm (71) are, in some examples, mounted in opposition, i.e. with angularoffset of 180 degrees, as can be seen more clearly in FIG. 7 b. When thecommon motor (M3) is operated for imparting a rocking or oscillationmotion to the arm (52) and to the arm (71), this can ensure that, duringeach forward or return movement, the arm (71) will pass over the biomasspreviously poured onto the bed (80) of biomass by the arm (52) of thepusher. This gives very good equalization of the surface of the bed ofbiomass in the pyrolysis zone, which improves the pyrolysis reaction.

FIGS. 8 a and 8 b show a front section and a cross section,respectively, of another example gasifier according to the teachings ofthis disclosure. Here, the example plate is formed by a fixed plate (50)which extends substantially over the whole cross section of the vessel(4). The plate (50) is equipped with at least one opening (58) throughwhich the pusher (52) can push the fuel (2) retained by the plate sothat the fuel (2) falls by gravity into the pyrolysis zone (10). Theopening (58) is offset relative to the means of admission (5) so thatthe fuel cannot fall directly into the pyrolysis zone. Otherwise thisgasifier is similar to those disclosed above.

As shown in FIG. 8 a, the motor (M3), in this example, is dispose andoperate outside of the vessel (4) to allow easier access to the motorand so that the motor is not subjected to the conditions prevailingwithin the vessel (temperature, presence of gases, etc.).

Many other forms of example plate and of the example pusher can beenvisaged, provided that the plate is able to retain the fuel deliveredby the feeding means (5) and that the pusher (52) is able to push theretained fuel and cause the fuel to fall by gravity onto the pyrolysiszone (10).

The teachings of this disclosure also relate to a unit for productionand combustion of gas, comprising a gasifier as disclosed and/or claimedin the present application. The example unit may be, for example, anassembly that includes a gasifier as disclosed above and aninternal-combustion engine, the outlet (6) of the gasifier beingconnected to a fuel admission system of the internal-combustion engine.

The present disclosure has been described in relation to specificexample that are given purely for purposes of illustration and must notbe regarded as limiting. Generally a person skilled in the art wouldunderstand that the present disclosure is not limited to the examplesillustrated and/or described and disclosed above.

The presence of reference numbers to the drawings cannot be regarded aslimiting, including when these numbers are stated in the claims.

The use of the verbs “comprise”, “include”, “contain”, or any othervariant, as well as their conjugations, does not in any way exclude thepresence of elements other than those mentioned.

The use of the indefinite article “a”, or the definite article “the”,for introducing an element does not exclude the presence of a pluralityof these elements.

The present disclosure can also be described as follows: a gasifier ofsolid carbon fuel (2) comprising at least one first vertical vessel (4)and feeding means (5) for introducing the fuel (2) into an upper part ofthe first vessel above a pyrolysis zone (10), the pyrolysis zone being azone where the fuel introduced undergoes pyrolysis to produce pyrolysisgases and carbonized fuel. The gasifier also comprises a combustion zone(20) for burning the pyrolysis gases, a reduction zone (30) forgasifying the carbonized fuel from the pyrolysis zone (10) in order toproduce synthesis gases and ash, and an outlet (6) for collecting thesynthesis gases. The first vessel (4) comprises a fixed horizontal plate(50) mounted between the feeding means (5) and the pyrolysis zone (10)so that the fuel introduced is retained there, as well as a movablepusher (51) mounted between the feeding means (5) and the plate (50) fortransferring the fuel retained on the plate to the pyrolysis zone (10).The plate (50) forms a thermal screen at least partially protecting thefeeding means (5) and the movable pusher (51) against the hightemperatures prevailing in the first vessel (4) when the latter is inoperation.

Although certain example methods and apparatus have been disclosedherein, the scope of coverage of this patent is not limited thereto. Onthe contrary, this patent covers all methods, apparatus and articles ofmanufacture fairly falling within the scope of the appended claimseither literally or under the doctrine of equivalents.

1. A gasifier comprising a vertical vessel comprising: feeding means forintroducing a fuel at a top and along a first vertical axis in thevessel; a pyrolysis zone for pyrolysis of the fuel; a combustion zonefor burning pyrolysis gases from the pyrolysis zone; a reduction zonefor gasifying carbonized fuel from the pyrolysis zone; an outlet forcollecting gases produced in the reduction zone; a horizontal platefixedly mounted between the feeding means and the pyrolysis zone forreceiving and retaining the fuel introduced into the vessel; and amovable pusher mounted between the feeding means and the horizontalplate, the movable pusher to push the fuel retained on the horizontalplate into the pyrolysis zone and positioned or positionable above thehorizontal plate.
 2. The gasifier as claimed in claim 1, wherein themovable pusher comprises at least one arm extending horizontally abovethe plate and mounted rotatably about a second vertical axis.
 3. Thegasifier as claimed in claim 2, wherein the second axis is offsetrelative to the first axis.
 4. The gasifier as claimed in claim 2,further comprising: a motor for driving the at least one arm of thepusher in rotation about the second axis; and first controlling meansfor controlling the motor to give a rocking motion to the at least onearm about the second axis.
 5. The gasifier as claimed in claim 4,wherein the first controlling means is to set an initial angularposition and an amplitude of the rocking motion.
 6. The gasifier asclaimed in claim 1, wherein the first vessel comprises levelling meansto at least partially level a top surface of a bed of solid fuel in thepyrolysis zone.
 7. The gasifier as claimed in claim 6, wherein thelevelling means comprises at least one levelling arm extendinghorizontally at a level of the top surface of the bed of solid fuel inthe pyrolysis zone, the at least one arm being mounted rotatably about athird vertical axis.
 8. The gasifier as claimed in claim 7, wherein thelevelling means comprises six arms mounted radially at intervals of 60degrees around a rotating shaft with the third axis.
 9. The gasifier asclaimed in claim 7, wherein the second axis and the third axis coincide.10. The gasifier as claimed in claim 9, wherein the at least one arm ofthe pusher and the at least one levelling arm of the levelling means aremounted on a rotating shaft.
 11. The gasifier as claimed in claim 3,further comprising: a motor for driving the at least one arm of thepusher in rotation about the second axis; and first controlling meansfor controlling the motor to give a rotating motion to the at least onearm about the second axis.
 12. The gasifier as claimed in claim 11,wherein the first controlling means is to set an initial angularposition and an amplitude of the rotating motion.
 13. The gasifier asclaimed in claim 8, wherein the second axis and the third axis coincide.14. The gasifier as claimed in claim 9, wherein the at least one arm ofthe pusher and the at least one levelling arm of the levelling means aremounted on a rotating shaft.
 15. A unit for production and combustion ofgas, comprising a gasifier as claimed in claim 1 for producing the gas.16. A gasifier comprising: an inlet to introduce a fuel; a pyrolysiszone to pyrolyze the fuel; a plate mounted between the inlet and thepyrolysis zone to hold the fuel; a pusher mounted between the inlet andthe plate to push the fuel from the plate into the pyrolysis zone, thepusher positioned above the plate and movable relative to the plate; acombustion zone to burn pyrolysis gases from the pyrolysis zone; areduction zone to gasify carbonized fuel from the pyrolysis zone; and anoutlet to collect gases produced in the reduction zone.